Edge transistor elimination in oxide trench isolated N-channel metal–oxide–semiconductor field effect transistors

Abstract

Bulk N-channel metal–oxide–semiconductor field effect transistors (MOSFETs) can suffer from parasitic edge transistor effects, unless several extra processing and masking steps are used. These edge devices increase the off-state current and degrade subthreshold slope of the N-MOSFETs. Parasitic edge transistors in oxide trench isolated N-MOSFETs, formed using selective epitaxial growth of silicon, were caused by the boron out-diffusion during high temperature process steps. Employing a simple ammonia nitridation of the field oxide before the epitaxial growth step, boron out-diffusion into the surrounding oxide was suppressed. The parasitic edge transistors in oxide trench isolated N-MOSFETs were eliminated.